CN101038259A - Method for measuring component of limestone CaCO3 and MgCO3. - Google Patents

Abstract

The invention belongs to the technical field of flue gas desulfurization, and discloses a method for measuring components of limestone CaCO ₃ and MgCO ₃ . The measurement steps of _CaCO3 are: (1) Dissolve limestone with hydrochloric acid; (2) Add KOH solution and calcium carboxylic acid indicator successively; (3) Titrate with EDTA standard solution until the color of the solution changes from red to blue, according to EDTA Calculating the _CaCO3 content with the titer of MgCO3; the measurement steps of _MgCO3 are: (1) dissolve the limestone with hydrochloric acid; (2) add ammonia solution and Merck indicator successively; (3) after the indicator is dissolved, use EDTA standard solution Titrate until the solution color changes from red to green; ( ₄ ) use ZnSO Standard solution to titrate excessive EDTA until the solution color changes back to red from green, according to EDTA standard solution and _ZnSO The titration of standard solution calculates the total amount of calcium and magnesium, by Calculate the content of MgCO ₃ by subtraction method. Compared with the national standard analysis method, the invention has the characteristics of simple operation, less reagents used, low cost, safe operation and the like.

Description

A kind of measurement lime stone CaCO 3, MgCO 3The method of composition

Technical field

The invention belongs to the flue gas desulfurization technique field, relate to a kind of measurement lime stone CaCO ₃, MgCO ₃The method of composition.

Background technology

Acid rain, greenhouse effect and depletion of the ozone layer are the human current three overall situation problems that face, and wherein acid rain is the problem that must at first be solved.The SO of burning mineral fuel discharging ₂It is the one of the main reasons that causes acid rain.Acid rain causes the acidifying of soil and water system, jeopardizes forests and crops, causes catastrophic effect for human ecologic environment.Since the early 1980's, along with the development constantly rapidly of China's economy, China's atmosphere is by SO ₂Severe contamination, SO ₂Discharge capacity reaches more than 2,000 ten thousand t, becomes world SO ₂The 1st big country of discharging.SO in China's atmosphere ₂94% from coal burning, according to nineteen ninety-five statistics, coal in China consumption 12.75 hundred million t/a, SO ₂Discharge capacity 2,370 ten thousand t/a estimate SO in 2010 ₂Discharge capacity will reach 3,300 ten thousand t/a.Therefore, acid rain problem be fundamentally solved, at first SO will be controlled ₂Discharging, reduce its pollution to environment, take effective measures control SO ₂Discharge very urgent.Eliminate SO ₂Pollution has three kinds of approach, desulfurization and flue gas desulfurization in i.e. desulfurization before the burning, the burning, wherein flue gas desulfurization is considered to effective way, and limestone-gypsum wet desulphurization technology is the most widely used technology of flue gas desulfurization technique, lime stone is as the desulfurizing agent in the flue gas desulfurization technique, and its quality has directly influenced the desulfuration efficiency of flue gas.The effective active composition of lime stone is CaCO ₃, its content has direct influence to desulfurization degree, so in engineering, we need carry out constituent analysis to multiple lime stone, filters out a kind of good lime stone as desulfurizing agent.

CaCO in the lime stone ₃, MgCO ₃Content be an important parameter estimating the lime stone quality, seek a kind of simple, safety, accurate analytical method is necessary.

Existing a kind of measurement lime stone CaCO ₃, MgCO ₃The method of composition is National Standard Method-chemical industry lime stone componential analysis (GB/T 15057.2-94).

1. required reagent of National Standard Method and solution have:

(1) hydrochloric acid (HCl, 1: 1 solution) is analyzed pure; Effect: the CaCO in the dissolving lime stone ₃, MgCO ₃,

(2) hydrofluorite (HF) is analyzed pure; Effect: the CaCO in the dissolving lime stone ₃, MgCO ₃

(3) perchloric acid (HClO ₄), analyze pure; Effect: the CaCO in the dissolving lime stone ₃, MgCO ₃

(4) triethanolamine (C ₆H ₁₅NO ₃, 1: 1 solution), analyze pure; Effect: shelter interference element such as Fe, Al in the lime stone.

(5) (KOH 200g/L), analyzes pure potassium hydroxide; Effect: the pH that keeps solution is more than 12.5;

(6) dextrin ((C ₆H ₁₀O ₅) _nXH ₂O 40g/L), analyzes pure; Preparation: take by weighing the 4g dextrin, water furnishing pasty state adds 100mL boiling water (preparation before using); Effect: the stability that keeps solution;

(7) oxammonium hydrochloride (HONH ₃Cl 50g/L), analyzes pure; Effect: some high volence metal ions are reduced to low valence metal ion, eliminate and disturb;

(8) ammonium chloride (NH ₄Cl): with ammoniacal liquor preparation ammonium chloride-ammoniacal liquor buffer solution (pH ≈ 10)

(9) ammoniacal liquor (NH ₃H ₂O): with ammonium chloride preparation ammonium chloride-ammoniacal liquor buffer solution (pH ≈ 10)

Take by weighing 67.5g ammonium chloride and be dissolved in the 300mL water, add 570mL ammoniacal liquor, move in the 1000mL volumetric flask, be diluted with water to scale, shake up; Effect: the pH value that keeps solution about 10,

(10) disodium ethylene diamine tetraacetate (C10H14N2O8Na22H2O), ethylenediaminetetraacetic acid

0.01mol/L the compound method of EDTA standard solution be: take by weighing the 4g disodium ethylene diamine tetraacetate, use dissolved in distilled water, move in the 1000mL volumetric flask, be diluted to scale, shake up.

0.01mol/L the scaling method of EDTA standard solution be:: take by weighing the benchmark zinc paste of 0.2g, be accurate to 0.0001g in 800 ℃ of calcinations to constant weight.Moistening with low amounts of water, add 20% hydrochloric acid solution and make sample dissolution, move in the 250ml volumetric flask, be diluted to scale, shake up.From volumetric flask, measure 25mL, add 70mL distilled water, be neutralized to PH7～8, add 10mL ammonium chloride-ammoniacal liquor damping fluid and 5 5g/L chromium black T indicators, with the disodium ethylene diamine tetraacetate standard solution [C for preparing with 10% ammonia spirit _EDTA=0.01mol/L] titration becomes pure blue to solution colour by purple and is terminal point; Do blank test simultaneously.

C _EDTA＝m/(V1-V2)*0.08138

The quality of m-ZnO (g) in the formula;

The consumption of V1---disodium ethylene diamine tetra-acetic acid solution, mL;

V2---the blank test consumption of disodium ethylene diamine tetraacetate, mL;

0.08138---the quality of suitable with 1.00mL disodium ethylene diamine tetraacetate standard solution [CEDTA=1.000mol/L] zinc paste with the gram expression.

0.01mol/L the effect of EDTA standard solution: with Ca ²⁺, Mg ²⁺Carry out complex reaction

(11) calcium carboxylate (C ₂₁H ₁₄N ₂O ₇S): mix with sodium chloride (NaCl) and to make indicator

(12) sodium chloride (NaCl): mix with calcium carboxylate and to make indicator

Take by weighing 1g calcium carboxylate (C ₂₁H ₁₄N ₂O ₇S) with sodium chloride (NaCl) porphyrize, the mixing of 105 ℃ of oven dry of 100g, be stored in the port grinding bottle, as the calcium carboxylate indicator

(13) acid chromium blue k indicator (C ₁₆H ₉N ₂Na ₃O ₁₂S ₃, 5g/L): take by weighing the 0.5g acid chromium blue k and be dissolved in (operating period is a week) in the 100mL water.Effect: colour developing

(14) the green B indicator of phenol (C how ₃₀H ₁₅FeN ₃Na ₃O ₁₅S ₃, 5g/L): take by weighing 0.5g how (operating period is a week) in the green 100mL of the being dissolved in water of phenol.Effect: colour developing

2. the measuring process of National Standard Method:

(1) preparation of sample solution

The lime stone sample more than 100 ℃ of dry 2h, places exsiccator to be cooled to room temperature by 125 μ m testing sieves.Take by weighing about 0.2g sample, be accurate to 0.0001g (A[mg]), place the 100mL polytetrafluoroethylene beaker, do blank contrast test simultaneously, with the wetting sample of little water (about 5mL), cover surface plate, drip HCl solution (1: 1) along the beaker mouth, treat that vigorous reaction stops after, excessive 1mLHCl solution, with distilled water flushing surface plate and walls of beaker, add 4mL hydrofluorite HF and 2mL perchloric acid HClO ₄, place on the electric hot plate low-temperature heat closely dried, take off beaker, cold slightly, wash wall of cup with little water, continue the heating white cigarette and emit to the greatest extent to doing; Cold slightly, add 3mLHCl solution, heating for dissolving is cooled to room temperature to refrigerant, moves in the 250mL volumetric flask, is diluted with water to scale, shakes up.

(2) CaCO ₃Mensuration

The sample solution of drawing 25mL (vol.[mL]) step (1) preparation places the 250mL conical flask, adding distil water 100mL, dextrin solution 10mL, triethanolamine solution 5mL, KOH solution 15mL, make pH value of solution greater than 12.5, add a little calcium carboxylate indicator (about 0.2-0.4g), shake up, become pure blue to solution colour by claret with the EDTA standard solution titration and be terminal point (B[mL]), the volume that blank test consumes is (E[mL]).

CaCO ₃[％]＝C _EDTA(B-E)*0.1001*250*100/A/vol.

(3) MgCO ₃Mensuration

The sample solution of drawing 25mL (vol.[mL]) step (1) preparation places the 250mL conical flask, adding distil water 100mL, oxammonium hydrochloride 5mL, triethanolamine 5mL, ammonium chloride-ammoniacal liquor buffer solution 10mL, 2-3 drip acid chromium blue k indicator and 6-7 and how to drip the green B indicator of phenol, shake up, become bright green to solution colour by kermesinus with the EDTA standard solution titration and be terminal point (C[mL]), the volume that blank assay consumes is (F[mL]).

MgCO ₃[％]＝C _EDTA[(C-F)-(B-E)]*0.08431*100*250/A/vol.

3. the theoretical foundation of National Standard Method

Lime stone CaCO ₃, MgCO ₃The theoretical foundation of constituent analysis: lime stone is (shown in reaction equation 1,2) behind dissolving with hydrochloric acid, successively adds KOH solution in solution, the calcium carboxylate indicator, and in the solution of pH＞12.5, Mg ²⁺Become Mg (OH) ₂Form precipitation (shown in reaction equation 3), and Ca ²⁺Do not form precipitation, it and calcium carboxylate indicator form a kind of complex compound (shown in reaction equation 4), and at this moment, solution is claret, and behind titration EDTA, EDTA can capture Ca from complex compound ²⁺And making the calcium carboxylate indicator free, solution colour becomes just au bleu (shown in reaction equation 5) by claret, so just can calculate CaCO in the lime stone according to the titer of EDTA ₃Content;

In the solution of pH ≈ 10, Ca ²⁺, Mg ²⁺All do not become precipitation, but generate a kind of complex compound (shown in reaction equation 6) with indicator (acid chromium blue k and how the green B of phenol), at this moment, solution is kermesinus, and behind titration EDTA, EDTA can capture Ca from complex compound ²⁺, Mg ²⁺And make indicator free, and solution colour becomes bright green (shown in reaction equation 7) by kermesinus, just can calculate calcium magnesium total amount according to the titer of EDTA standard solution, and the content of being tried to achieve magnesium by minusing is MgCO ₃Content.

CaCO ₃+2HCl＝CaCl ₂+H ₂O+CO ₂↑ (1)

MgCO ₃+2HCl＝MgCl ₂+H ₂O+CO ₂↑ (2)

Mg ²⁺+2OH-＝Mg(OH) ₂↓ (3)

Ca ²⁺+ calcium carboxylate → Ca-calcium carboxylate (claret) (4)

Ca-calcium carboxylate (claret)+EDTA → Ca-EDTA+ calcium carboxylate (pure blue) (5)

Ca ²⁺+ Mg ²⁺+ indicator → Ca-indicator+Mg-indicator (kermesinus) (6)

Ca-indicator+Mg-indicator (kermesinus)+EDTA → Mg-EDTA+Ca-EDTA+ indicator (bright green) (7)

4. the deficiency of National Standard Method

This measuring method has advantages such as analysis result is accurate, but has the following disadvantages:

(1) preparation process of lime stone sample solution is complicated, and the acid chromium blue k indicator, how the operating period of medicine such as the green B indicator of phenol can only be kept a week, so need preparation again before each the analysis, relatively waste.

(2) sample making course relates to hazardous chemicals such as HF and HClO ₄, very harmful to human body.

Hydrofluorite: the people takes in 1.5g hydrofluorite can cause death immediately; The hydrofluorite acid mist that sucks high concentration causes bronchitis and hemorrhagic pulmonary edema; The hydrofluorite acid mist also can cause pruitus and dermatitis, also can cause burning of skin, intestines and stomach and respiratory mucosa when dosage is big; Hydrofluorite easily causes serious poisoning after skin absorbs.

Perchloric acid: the acidity of perchloric acid is higher than sulfuric acid and nitric acid, is a kind of transparency liquid, can be fuming strongly in air, has extremely strong corrosivity; Fire goods such as paper, charcoal are dropped into perchloric acid, can cause burning even blast at once; Perchloric acid is heated and easily decomposes, and temperature surpasses 90 ℃ and can blast; If splash perchloric acid, can cause and burn on the skin.

In the GB analytic approach, therefore skin bad phenomenon such as eyes redness once just appearred in our chemical analysis personnel.

(3) the required reagent of analytic process is many, needs 14 kinds of reagent and solution, and cost is higher relatively.

(4) when titration calcium magnesium total amount, the color of solution becomes bright green by kermesinus, and titration end-point is difficult to distinguish, and is bigger to the titration results influence.

Summary of the invention

Purpose of the present invention mainly is to measure lime stone CaCO at prior art ₃, MgCO ₃The deficiency of compositions, method, propose a kind of simple to operate, agents useful for same is few, cost is low, the measurement lime stone CaCO of handling safety ₃, MgCO ₃The method of composition.

The present invention realizes by following scheme:

CaCO ₃Measuring process be: (1) is with the lime stone dissolving with hydrochloric acid; (2) successively add KOH solution, calcium carboxylate indicator; (3) become blueness with EDTA standard solution titration to solution colour by redness, according to the titer calculating CaCO of EDTA ₃Content;

MgCO ₃Measuring process be: (1) is with the lime stone dissolving with hydrochloric acid; (2) successively add ammonia spirit, Merck indicator; (3) treat indicator dissolving after, become green with EDTA standard solution titration to solution colour by redness; (4) use ZnSO ₄The excessive EDTA of standard solution titration becomes redness again by green to solution colour, according to EDTA standard solution and ZnSO ₄The titer of standard solution calculates calcium magnesium total amount, tries to achieve MgCO by minusing ₃Content.

The advantage of the inventive method is mainly reflected in the following aspects:

(1) preparation process of lime stone sample solution is oversimplified.

(2) sample making course does not relate to HF and HClO ₄Deng hazardous chemicals, operate more complete.

(3) 7 kinds of (14 kinds of National Standard Method) costs of the required reagent of The whole analytical process are corresponding also reduces.

(4) more or less freely the distinguishing of whole titration process change color.

(5) favorable reproducibility of test findings.

Embodiment

Reagent required for the present invention:

(1) hydrochloric acid (HCl, 30%) is analyzed pure; Effect: the CaCO in the dissolving lime stone ₃, MgCO ₃

(2) (KOH 0.25g/mL), analyzes pure potassium hydroxide; Effect: keep pH value of solution more than 12.5;

(3) ammoniacal liquor (NH ₃H ₂O, 5%), analyze purely, effect: the pH that keeps solution is about 10

(4) disodium ethylene diamine tetraacetate (C ₁₀H ₁₄N ₂O ₈Na ₂2H ₂O, 0.1mol/L (needing to demarcate), ethylenediaminetetraacetic acid), preparation is as follows with scaling method:

0.1mol/L disodium ethylene diamine tetraacetate preparation: take by weighing the 40g disodium ethylene diamine tetraacetate, use dissolved in distilled water, move in the 1000mL volumetric flask, be diluted to scale, shake up.

0.1mol/L disodium ethylene diamine tetraacetate is demarcated: take by weighing the benchmark zinc paste of 0.25g in 800 ℃ of calcinations to constant weight, be accurate to 0.0001g.Moistening with low amounts of water, the hydrochloric acid solution that adds 2mL 20% makes sample dissolution, adds 100mL distilled water, and being neutralized to pH value with 10% ammonia spirit is 7 ∽ 8, add 10mL ammonium chloride-ammoniacal liquor damping fluid and 5 chromium black T indicators, with the disodium ethylene diamine tetraacetate standard solution [C for preparing _EDTA=0.1mol/L] titration becomes pure blue to solution colour by purple and is terminal point; Do blank test simultaneously.

C _EDTA＝m/(V1-V2)*0.08138

The quality of m in the formula---zinc paste, g;

The consumption of V1---disodium ethylene diamine tetra-acetic acid solution, mL;

V2---the blank test consumption of disodium ethylene diamine tetraacetate, mL;

0.08138---with 1.00mL disodium ethylene diamine tetraacetate standard solution [C _EDTA=1.000mol/L] quality of suitable zinc paste with the gram expression.

(5) zinc sulfate (ZnSO ₄, 0.1mol/L (needing to demarcate):

0.1mol/L ZnSO ₄The preparation of standard solution and demarcation:

0.1mol/L ZnSO ₄The standard solution preparation: take by weighing 15g zinc sulfate, the water dissolving moves in the volumetric flask of 500mL, is diluted to scale.

0.1mol/L ZnSO ₄Standard solution is demarcated: measure the solution of zinc sulfate that 25mL prepares, add 70mL distilled water and 10mL ammonium chloride-ammoniacal liquor buffer solution (PH ≈ 10), add 5 eriochrome black T indicator solutions, use C _EDTABecome blueness by purple and be terminal point for the standard solution of 0.1mol/L carries out titration to the color of solution, do blank test simultaneously.

C _ZnSO4＝C _EDTA*(V1-V2)/V

In the formula, C _ZnSO4---the zinc sulfate standard solution concentration, mol/L

The consumption of V1---disodium ethylene diamine tetra-acetic acid solution, mL;

V2---the blank test consumption of disodium ethylene diamine tetraacetate, mL;

The volume of V---the solution of zinc sulfate that pipettes, mL

C _EDTA---the concentration of disodium ethylene diamine tetra-acetic acid solution, mol/L

(6) calcium carboxylate: mix with sodium sulphate and to make the calcium carboxylate indicator

(7) sodium sulphate: mix with calcium carboxylate and to make the calcium carboxylate indicator

Take by weighing calcium carboxylate and the 10g sodium sulphate of 0.1g, porphyrize, mixing is stored in the port grinding bottle.

Assay method:

1. the preparation of sample solution

The lime stone sample more than 100 ℃ of dry 2h, places exsiccator to be cooled to room temperature by 125 μ m testing sieves; Take by weighing about 2g sample, be accurate to 0.0001g (A[mg]), place the beaker of 250mL, do blank assay simultaneously, add the wetting lime stone of little water (about 5mL), cover surface plate, dropwise drip 30% HCl 10mL along the beaker mouth, fully shake up, in beaker, add 100mL distilled water then, be heated to little boiling, and keep slight boiling condition 30min; Carry out suction filtration after the cooling, wash wall of cup repeatedly to the filtrate till the anacidity, change over to all filtrates in the 250mL volumetric flask then and be diluted to scale;

2.CaCO ₃Mensuration

The sample solution (vol.[mL]) that pipettes 5mL step (1) preparation is in the 250mL conical flask, adding distil water 100mL, 0.25g/mL KOH solution 2mL, add a little calcium carboxylate indicator (about 0.2-0.4g), carrying out titration with the EDTA standard solution of 0.1mol/L then becomes blueness to solution colour by redness and is terminal point, write down the volume (F[mL]) of consumption, the volume that blank assay consumes is (B[mL]).

CaCO ₃[％]＝(F-B)*C _EDTA*100.04*100*250/A/vol.

3.MgCO ₃Mensuration

The sample solution (vol.[mL]) that pipettes 5mL step (1) preparation is in the 250mL conical flask, adding distil water 100mL, 5% ammonia spirit 5mL, add a slice Merck indicator again, after treating the indicator dissolving, become green with EDTA standard solution titration to solution colour by redness, write down the volume (D[mL]) of consumption, and then use ZnSO ₄The excessive EDTA of standard solution titration becomes redness to solution colour again by green and is terminal point (E[mL]).

MgCO ₃[％]＝D*C _EDTA-E*C _ZnSO4)-(F-B)*C _EDTA]*84.31*250*100/vol./A

Experimental result

Measuring method of the present invention and existing National Standard Method have been carried out the contrast experiment, respectively three samples have been analyzed, experimental result is as follows:

Table 1 the inventive method and National Standard Method are analyzed the experimental result contrast of lime stone composition

Sample	CaCO 3(％)		MgCO 3(％)
					National Standard Method	The inventive method	National Standard Method	The inventive method
	Sample one sample two samples three	94.33 93.52 97.3	93.27 92.4 95.7	2.52 2.35 2.21					2.46 2.30 2.18

From test result, the errors of analytical results of two kinds of analytical approachs is at 1%-2%, on the whole, and the CaCO that National Standard Method is measured ₃(%) content is higher, this be because: used hydrofluorite and perchloric acid in the National Standard Method, their dissolving power extra-heavy can be some non-CaCO in the lime stone ₃The Ca that form exists has dissolved (CaCO ₃Be the effective active composition of lime stone, and the effective active component of Ca right and wrong that other forms exist) so CaCO ₃Content is higher, and from this on the one hand, the result of employing the inventive method test is more reliable, more is applicable in the engineering and uses, because it does not use hydrofluorite and perchloric acid, what adopt the inventive method dissolving just is with CaCO ₃The Ca that form exists, i.e. effective active composition.

The reappearance of the inventive method is fine.We have carried out repeatedly analyzing to same sample, and analysis result is as follows:

The reappearance of table 2 the inventive method

Analysis project	Same sample
				For the first time	For the second time	For the third time
	CaCO 3(％) MgCO 3(％)	95.7 1.81	95.6 1.99				95.4 2.08

From analysis result: the component content that same sample different time is measured is very approaching, particularly CaCO ₃Content, this has proved absolutely favorable reproducibility, the good stability of this method.

Claims (1)

1. measure lime stone CaCO for one kind ₃, MgCO ₃The method of composition is characterized in that

CaCO ₃Measuring process be: (1) is with the lime stone dissolving with hydrochloric acid; (2) successively add KOH solution, calcium carboxylate indicator; (3) become blueness with EDTA standard solution titration to solution colour by redness, according to the titer calculating CaCO of EDTA ₃Content;

MgCO ₃Measuring process be: (1) is with the lime stone dissolving with hydrochloric acid; (2) successively add ammonia spirit, Merck indicator; (3) treat indicator dissolving after, become green with EDTA standard solution titration to solution colour by redness; (4) use ZnSO ₄The excessive EDTA of standard solution titration becomes redness again by green to solution colour, according to EDTA standard solution and ZnSO ₄The titer of standard solution calculates calcium magnesium total amount, tries to achieve MgCO by minusing ₃Content.